1. Field of the Invention
The present invention relates to a printing apparatus and a registration adjustment method used in the apparatus, and particularly to, for example, a printing apparatus including a plurality of inkjet printheads and a registration adjustment method used in the apparatus.
2. Description of the Related Art
A printing apparatus including an inkjet printhead (to be referred to as a printhead hereinafter) forms dots on a print medium by discharging ink droplets from the printhead, and forms an image by the dots. A dot alignment technique between different conditions is called a registration correction technique, and alignment of dots is implemented by acquiring and applying a correction value.
A method of acquiring this correction value by visually observing a printed pattern by the user, and applying that correction value, a method of reading a printed pattern by a sensor included in a printing apparatus, and executing automatic adjustment, and the like are available.
As one automatic adjustment method, a method of directly detecting a position shift distance of patterns formed under a plurality of printing conditions using a sensor, and acquiring that distance as a correction amount is known. This method is called a range detection method.
For example, Japanese Patent Laid-Open No. 2009-56746 has proposed a conventional registration adjustment method.
In a printer which executes printing on a print medium of a large size such as an A0 or B0 print sheet by reciprocally scanning a carriage that mounts a printhead, it is difficult to maintain a stable state all over that scanning region.
External disturbances which influence stable printing include a variation of a distance between the printhead and print sheet, an attitude variation of the carriage, and the like. These external disturbances occur depending on a position in the carriage moving direction. For this reason, the apparatus state varies depending on a registration adjustment position, and a correction value cannot often be correctly calculated. Especially, in the range detection method, the influences caused by external disturbances occurred between a plurality of patterns used to compare position shifts often directly result in errors of the correction value.